1. Field of the Invention
This invention relates to a computer key construction, more particularly to a notebook computer key which has a more stable and durable construction.
2. Description of the Prior Art
There are, at present, two types of computer key constructions which are commonly used. The first type employs a microswitch that is attached to and actuated by a pressing action on a key cap. However, the size of this kind of computer key is relatively large and for this reason is seldom used in portable notebook computers.
The second type employs an electrical switch and is commonly used in portable notebook computers. Referring to FIG. 1, a conventional electric switch notebook computer key comprises a push button (A), a slightly convex support member (B), a resilient biasing member (C), a socket member (D) and a circuit board (E). The push button (A) has a slightly concave top portion (A1) with a downwardly extending peripheral flange (A2). A mounting projection (A3) extends downward from the rear side of the top portion (A1) to secure the push button (A) on the support member (B). The socket member (D) has an upwardly extending confining wall (D1) which defines a receiving space (D3) to receive the support member (B). The top edge of the confining wall (D1) is provided with an upwardly curving flange (D2) which corresponds with the shape of the support member (B). The support member (B) has one end provided with a downwardly extending flange (B1) which abuts the inner surface of the confining wall (D1). The support member (B) also serves as a dust protection layer to prevent dust from collecting on the circuit board (E). The resilient biasing member (C) is made of rubber and has a tubular support portion (C1), the top end of which abuts the rear side of the support member (B), while the bottom end of the same supports a conductive member (C4). The outer surface of the support portion (C1) is connected to a downwardly extending and gradually expanding cover portion (C2) that confines a receiving space (C5). The resilient biasing member (C) further includes a horizontally disposed cushion layer (C3) connected to the bottom edge of the cover portion (C2). The resilient biasing member (C) is provided on top of the circuit board (E). The bottom end of the confining wall (D1) tightly abuts the cushion layer (C3) to secure the biasing member (C) onto the circuit board (E). The portion of the circuit board (E) inside the receiving space (C5) is provided with silver powdery conductive strips (E1).
When the push button (A) is pressed, the support member (B) moves downward to compress the biasing member (C) and move the conductive member (C4) to contact the conductive strips (E1) on the circuit board (E) to signal a pressed key condition. When the applied force is released, the biasing member (C) expands to once more move the conductive member (C4) away from the conductive strips (E1) and break the electrical connection.
From the foregoing, it has been shown that the biasing member (C) provides the necessary force to return the push button (A) from the pressed key position to the initial unpressed key position. However, the elastic properties of the biasing member (C) gradually wears down after prolonged use of the above described computer key. Thus, the push button (A) cannot be properly returned to the initial unpressed key condition. Operation of the computer key eventually becomes impossible since the conductive member (C4) gradually comes into contact with the circuit board (E) because of wearing of the biasing member (C). Furthermore, because of the construction of the biasing member (C), the height of the computer key shown in FIG. 1 should be at least 14.00 mm, while the vertical distance traveled by the push button (A) from the initial unpressed key position to the pressed key position is generally at 3.5 mm.